Intravenous drug abusers (IVDAs) are a major target for the spread of HIV in Spain. A prevalence rate of 8-15% of HIV antibodies among partners of IVDAs, although higher rates have been suggested since a substantial proportion of these people may be latently infected. The presence of latent HIV infection was investigated by PCR. Genomic DNA was prepared from (PBMCs) of 32 seronegative partners of IVDAs and 5 partners of seropositive regions. Primers were derived from the gag (SK38/39) and env (68/69) regions. All samples were also tested for HIV antigenaemia. 11/32 heterosexual partners of IVDAs and 5 partners of seropositive promiscuous subjects. 11 of 32 heterosexual partners of IVDAs as positive for gag sequences by PCR. 3 were positive for env sequences. All 5 heterosexual partners of the promiscuous infected subjects were positive, but 4 also had HIV antibodies. The 13 subjects who were positive by PCR but did not have antibodies to HIV were negative for HIV antigen. Our study suggests that there may be a high proportion of silent HIV infection in Spanish IVDAs. We are at present evaluating the prevalence in larger population of IVDAs and homosexual men and their partners who remain seronegative.